CS 363 Comparative Programming Languages

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CS 363 Comparative Programming Languages

• Introduction

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Chapter 1 Topics

• Motivation
• Language Paradigms
• Programming Domains
• Language Design and Evaluation
• Influences
• Tradeoffs
• Implementation options

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Programming Languages

• Languages are
• an abstraction used by the
• programmer to express an idea
• interface to the underlying
• computer architecture

Sebesta Fig. 1.2
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Why study Programming Languages?

• Increases ability to express ideas in a language
• wide variety of programming features
• Improves ability to choose appropriate language
• Each language has strengths and weaknesses in
  term of expressing ideas
• Improves ability to learn new languages
• different paradigms, different features
• What does the future of programming languages
  hold?
• Improves understanding of significance of
  implementation
• Provides ability to design new languages
• Domain specific languages increasingly popular

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Language Paradigms

• Imperative
• Central features are variables, assignment
  statements, and iteration
• Ex C, Pascal, Fortran
• Object-oriented
• Encapsulate data objects with processing
• Inheritance and dynamic type binding
• Grew out of imperative languages
• Ex C, Java
• Functional
• Main means of making computations is by applying
  functions to given parameters
• Ex LISP, Scheme, Haskell

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Language Paradigms

• Logic
• Declarative ? Rule-based implicit control flow
• Ex Prolog
• Dataflow
• Declarative ? Model computation as information
  flow implicit control flow
• Inherently parallel
• Event-Driven
• Continuous loop with handlers that respond to
  events generated in unpredictable order, such as
  mouse clicks
• Often an add-on feature
• Ex Java
• Concurrent
• Multiple interacting processes
• Often an add-on feature
• Ex Java, High Performance Fortran (HPF), Linda

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Programming Domains

• Scientific applications
• One of the earliest uses of computers
• Large number of floating point computations
• Long running
• Imperative (Fortran, C) and Parallel (High
  Performance Fortran)
• Business applications
• Produce reports, use decimal numbers and
  characters
• Increasingly toward web-centric (Java, Perl,
  XML-based languages)
• Imperative (Cobol) and domain specific (SQL)
• Artificial intelligence
• Model human behavior and deduction
• Symbol manipulation
• Functional (Lisp) and Logical (Prolog)
• Systems programming
• Need efficiency because of continuous use
• Parallel and event driven
• Imperative (C)

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Language Design

• Principles of Design
• Influences on Design
• Evaluation of a design

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Principles of Language Design

• Basic Vocabulary
• Syntax what constitutes a correctly written
  program
• Type Systems and Semantics these allow us to
  provide a meaning to a syntatically correct
  program.
• Memory management data mapping, static and
  dynamic memory, stack, heap, object lifetime,
  garbage collection
• Exception handling how to deal with unexpected
  problems at runtime

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Influences on Language Design

• Von Neumann architecture Data and programs
  stored in same memory
• Memory is separate from CPU
• Instructions and data are piped from memory to
  CPU
• Basis for imperative languages
• Variables model memory cells
• Assignment statements model piping
• Iteration is efficient

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Influences on Language Design

• Programming methodologies
• 1950s and early 1960s Simple applications worry
  about machine efficiency
• Late 1960s People efficiency became important
  readability, better control structures
• Structured programming
• Top-down design and step-wise refinement
• Late 1970s Process-oriented to data-oriented
• data abstraction
• Middle 1980s Object-oriented programming

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Influences on Program Design

• Special Purpose (Domain Specific)
• Abstraction closer to problem domain
• Personal Preferences
• terse vs. verbose
• recursion vs. iteration
• user controlled vs. language controlled dynamic
  allocation

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Language Evaluation Criteria

• Readability most important!
• Overall simplicity
• Orthogonality A relatively small set of
  primitive constructs that can be combined in a
  relatively small number of ways
• Makes the language easy to learn and read
• Meaning is context independent
• Every possible combination is legal
• Lack of orthogonality leads to exceptions to
  rules
• Control statements
• Defining data types and structures
• Syntax considerations identifier forms, special
  words, meaning

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Language Evaluation Criteria

• Writability
• Simplicity and orthogonality
• Support for abstraction
• Expressivity
• Reliability
• Conformance to specs.
• Type checking
• Exception handling
• Aliasing
• Readability and writability

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Language Evaluation Criteria

• Cost
• Categories
• Training programmers to use language
• Writing programs
• Compiling programs
• Executing programs
• Language implementation system
• Maintaining programs (readability)
• Safety prevention of unchecked errors
• Others portability, generality, well-definedness

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Language Implementation Options

• Compilers
• Interpreters
• Hybrid options

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Compilers
Syntactic/semantic structure
tokens
Syntactic structure
Scanner (lexical analysis)
Parser (syntax analysis)
Semantic Analysis (IC generator)
Code Generator
Source language
Machine language
Code Optimizer
Input Data
Computer
Symbol Table
Output
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Interpreters
Interpreter
Source language
Output
Input Data
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Compilation vs. Interpretation

• Compilation
• Translate HL code directly into machine
• Translation can be slow
• Resulting code is fast (typically optimized)

• Interpretation
• Execute HL code directly
• No translation costs
• Execution can be slow

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Hybrid
tokens
Syntactic structure
Scanner (lexical analysis)
Parser (syntax analysis)
Semantic Analysis (IC generator)
Source language
Input Data
Intermediate Code
Interpreter
Symbol Table
Output
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What makes a language successful?

• Expressive Power
• Included features impact programmer use
• Ease of use for Novice
• Pascal, Basic, Logo
• Ease of Implementation
• Excellent Compilers
• Economics, Patronage, Legacy